Let me see if I remember clearly...
I believe Shedinja is only affected by fire, dark, ghost, flying, and rock attacks and things like sandstorm or spikes.
If you keep him away from these and UV train in attack or sp attack, he will be a great sweeper, mine is.

Rotom is alright because of his levitation (can't get hit by super effective ground attacks) and nice move pool, but he's nothing too great.

Always use a focus sash with shedninja, and focus just in attack, it doesnt have a special worth mentioning in public. Speed and Attack, likely any attack or speed boosting nature (that doesn't hinder the speed or the attack) will be fine, because his defenses dont matter...

Rotom is kinda cool, but should only be used with extreme skill, avoid it till you think you can use it properly